The present invention relates to radar reflectors and, more particularly, to a radar reflector which can be pulsed to transmit information.
In a variety of applications, it is desirable to use reflectors which are sized and shaped to serve as effective radar signal reflectors. One common example of such applications is in the delineation of the edges of airport runways.
Aircraft landings are made under a variety of visibility conditions. When visibility is adequate, the pilot is able to visually see the actual runway during daylight landings, or, in the case of nighttime landings, the pilot is able to visually see the various lights delineating the runway which are available in many airports. The inclusion of the human pilot into the landing control loop is considered to be highly desirable, albeit not indispensable.
For decades it has been possible to execute safe landings even in very limited visibility or no visibility at all. Such instrument landings typically rely on a radar system and an altimeter to replace the pilot's eyes in providing information about the relative position of the aircraft and runway in guiding the aircraft to a safe landing. In one common system, radar signals transmitted by the aircraft are reflected from special reflectors typically mounted at regular intervals near the edges of the runway. The reflected signals are received by the aircraft, outlining the runway on the pilot's radar screen.
The reflectors may have any convenient shape which will effectively reflect a large fraction of the impinging radar signals back to the aircraft using a relatively small reflector. One such reflector which is currently in widespread use is the comer reflector which, in one form, is in the shape of a tetrahedron having three radar-reflecting triangular walls connecting each set of three apices except for one set which remains open or which is connected by a radar-transparent material. The reflector is mounted so that the side of the reflector not including a reflecting wall generally faces the oncoming aircraft.
A difficulty with the use of such radar reflectors is that, in some circumstances, the runway may lie in an area which offers a large number of unintended radar reflectors. As a result, the pilot may see on his radar screen a large number of dots, only some of which are the specially mounted reflectors, and may become confused as to the actual location of the runway. A related problem is caused when spurious signals or other noise appears on the radar screen. To reduce or overcome this difficulty it may be necessary to either to clear the areas in the vicinity of the runway of some or all of the unintended radar reflectors, upgrade the electronics of the aircraft's radar systems and/or use a relatively large number of reflectors, relatively closely spaced, so as to produce a very clear line of dots on the pilot's radar screen. Either option significantly raises the cost of the radar reflector system.
There is thus a widely recognized need for, and it would be highly advantageous to have, a radar reflector system, which includes radar reflectors which would effectively and clearly delineate a runway, even amidst various unintended radar reflectors in the vicinity and noisy radar reception and which would not necessitate the use of a large number of closely spaced reflectors.